Modern military procurement typically requires development of a family of systems in order to gain approval. Therefore, it is often desirable in military applications to provide modularized systems that can be utilized in numerous embodiments while maintaining broad applicability. For example, the Future Combat Systems (FCS) Manned Ground Vehicle (MGV) will share a common architecture that focuses on high performance, commonality, and reliability. Control systems that are used on military vehicles such as the MGV vary widely depending on the assigned task. More specifically the servo control system must be capable of driving widely varying motor loads encountered in a family of military vehicles. Moreover, the servo control must be lightweight and have a small volume. The FCS system will incorporate many servo controlled motors and actuators. For example, the Non-Line of Sight (NLOS) cannon requires motor/actuator control for index magazine, close breech, raise load arm, track gun sight and other operations.
To move an object and position it at a predetermined location, a servomotor and servo control circuit are required as motive sources for obtaining a rotational position, velocity, torque and the like, which are in accordance with commanded data. Servo control is executed to produce an output based on a comparison between an externally applied command signal input and a feedback signal indicative of the state of the servomotor.
A variety of brushless DC and AC induction motors are commonly used in this type of military servo control application. Typically, the motors used in these applications are controlled by commutating the current supplied to the stationary windings. Rotor position sensors are usually included as an integral part of the motor and provide the controller with signals that indicate the position of the rotor magnets relative to the stator windings. To achieve high efficiency, control of the motor current is accomplished by pulse-width modulating solid state switches, usually power-switching transistors.
To accurately and reliably control the current as required in such an application, military servo control systems employ sensitive current sensors to determine real-time current flow to the servo motor. Typically, multiple current sensors will be used to measure a motor's primary and secondary windings, including individual phase windings. In the case of a Hall-based current sensor, a current-carrying wire is passed through, and wound around, a magnetic core, while a Hall effect sensor detects a magnetic field induced in the core. A number of factors may affect the accuracy of the current sensor, but the number of turns around the core is a primary factor.
When the servo control system controls multiple motors of different sizes, the number of different current sensors used in a system increases. One solution to this problem has been to simply sacrifice current sensing accuracy by using a current sensor optimized for a particular current, across a wide range of motor currents. This optimizes accuracy within a narrow range of measured currents, but seriously decreases accuracy at the outer ranges. In military servo control systems, sacrificing accuracy is usually not an option. Another solution has been to design and use different current sensors for each motor size. However, in military applications that value modularity and commonality, carrying an inventory of many different motor-specific current sensors is not a practical solution.
Accurately and reliably sensing high amperage motor current relies upon consistent, reliable operation of the greater servo control system. As such, another critical component of any servo control system is an efficient thermal management system. This is especially true in a military servo control system serving a wide range of high amperage servo motors.
Therefore, a need exists for a universal high-amperage current sensing system, along with a versatile thermal management system, that can accurately and reliably serve a wide range of servo motors in a greater servo control system.